In integrated circuit (IC) fabrication, metal lines (such as copper lines) are typically formed in ILD layers, where the ILD is often a porous silicon oxide based dielectric material or an organic dielectric material having a low dielectric constant, such as an ultra-low-k (ULK) dielectric. Formation of integrated circuits often requires patterning of the ILD to form vias and trenches, followed by subsequent filling of these vias and trenches with a metal (e.g., copper). After the vias and trenches are filled with a metal, a second layer of ILD is deposited, is patterned to form vias and trenches, and these recessed features are again filled with a metal, thereby resulting in a stack of ILD layers with embedded metal lines, where the metal lines form the conductive paths of an integrated circuit. Etch stop layers are often deposited over individual ILD layers, and are used in IC fabrication process to protect the material residing under the etch stop layer from being etched during patterning processes. For example, the semiconductor substrate may include an exposed first ILD layer, and an etch stop layer underlying the first ILD layer, and overlying a second ILD layer. The first ILD layer may be patterned and etched with a fluoride-based chemistry to define vias and trenches, while the etch stop layer protects the first ILD layer from being etched.
The etch stop layer material preferably should exhibit good etch selectivity versus the material that is being etched, that is, the etch stop layer material should preferably be etched at a significantly lower rate than the exposed ILD material.
The etch stop layer material typically is not completely removed during the integrated circuit fabrication, and remains in the final manufactured semiconductor device as a thin layer between thicker ILD layers. Examples of conventionally used etch stop layer materials include silicon carbide and silicon nitride. Because the etch stop layer remains in the manufactured semiconductor device its electrical properties are important. Specifically, etch stop layers with low leakage current are desired.